Transformer regulation.



E. 0. SCHWEHZEH.

TRANSFORMH; REGULAUGN.

APPLICATION FiLEU DEC. 7. 1910.

w Q MINSA@ @WSN L uw ZEP v 111V .Edmund Euhw EL ieg Wl nas MMM EBMUNB G. SCHWJ" EGULATIGN.

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Specification of )Letters latent.

Application file-. Beeeraber 7, 391e. Serial 11 o. 596,@53.

T0 ZZ whom 'it may concern Be it known that l, EDMND t). Sorwnrr znn, a citizen of the United tat-es, residing at Chicago, in the county of Cool; and tritate of Illinois, have invented certain new and useful limproveinents in Transformer 'Regulation, of which the following isa full7 clear7 concisefand exact descriptiom reference being had to the accompanyingI drawings, forming a part of this specification.

My invention relates to alternating` cnn rent transformers of electricity.

For various reasons well known to the ar it is desirable that the pressure on electric power and lightingl circuits he maintained as nearly constant as is feasible. lv'ly invention provides a combination which contributes toward thisultimate results while at the same time permitting1 the use of an .alternating current transformer which will withstand the electrical shochs flue to short circuits or other accidents to the circuits supplied. p

Transformers hav-e a certain natural lation, but cannot have in and them any means of regulation to tah'e care of flue* tuations in the line voltage. While a transformer may be made to have a very high regulation upon loads of unity power factor I have found it desirable in large installations to forego such high regulation in `order that the transformer may be constructed to withstand shocks such as are caused by short circuits. ilfhen, lmwevcrt the transformer .is constructed in sue.) a way as to prevent damage to the windings on account of such short circuits it is necessary to give the transformer a large iinpedance drop. When the impedance drop of the transformer is thus incre; sed to, say, live per cent. (5%), with full load currentj the regulation will be very much impaired. )Vhi'le such a transformer may have about two per cent. (2%) regulation al full load with unity power factor, it is geni-wally nccessary to provide against the effect which will he had when large induction motors are started and against the effect of a poor l power factor on ordinary commercial loads.

Nhere a fair percentage of the current is consumed in power motors.y the regulation of a transformer having this large impedance drop is certain to fall heloiY the limits of good commercial practice. 1When to the' drop of a transformer having this poor reg-I ulation is added the resistance "drop of a fici-oss the. bus bars l connect long line, the regulation of the system may become intolerable even if the pressure at the generating station is regulated better than two per cent. (2%).

ln accordance with my invention. l provide, in the jrst place. a transfornrr which is designed Lo have a large leakage of magnetic lines of force which do not link both primary and secondary windings; the primary and secondary windings are in other words not closely interlaced. rlhis leakage is made suilicient to produce an impedance drop of, say., per cent. (5%) on full load current. Such a transformer is likely lo withstand .the shocks incident th short circuits without damage to the windings. IOne or more transformers of this construction .may be connected to buses with which the stribut-ingr or load circuits are connected. synchronous motor. wound and connected for the same number ofphases as are the previously mein tioned transformers. if the direct current field of the synchronous motor be. suflici-cnlly strengthened the motor will piel; up a laidinfg; current. thus lreducingthe lag of the transformer current and improving the power factor of the transformer load. rlie size of the synchronous motor relative to the capacity of the transformers will depend somewhat upon the probable power factor of the load, and, although. havefound it unprol'itable to attempt to bring the power factor to unity, it is possible to do so by in stalling,` a synchronous motor of 'sufficient caparity; in fact, the whole load upon tie transformer can be made by this means to have a. leading power factor. Since the regulation of the transforn'xer or transformers is far better at or near unity power factor than on loads of flow power factor. a sv -hronous motor with constant field e5:- citation. of proper value will result in a large improvement .in the regulation of transformers supplyingA commercial loads in which a considerable percentage of the total energy is supplied4 for power purposes. )Vith constant field excitation the current taken up b v the synchronous motor will remainconstant, the, transformer being forced to take up the iiuctuations or variations in the load. rEhe line current will, of course, be reduced to an extent dependent upon the correct-ion of the power factor as edected by the 'synchronous motorfand this, ,alsol lwill result in an. improved regulation of transformer and line. To complete the combination of my invention I go further and provide an automatic mechanism to control the excitation of the synchronous motor. The excitation is controlled in such a way that any variations in the demand upon the transformer are compensated for by corresponding variations in the power factor effected through the agency of the s vf'nchronous motor. Not only does the automatic mechanism control the excitation of the synchronous motor to take care of variationsl in the load or demand upon the transforlmr, but also to take care of any fluctuations in the lpressure of the current. supplied from the generating station. This automatic regulating mechanism is arranged to act through the agencyof the exciter for the synchronous motor. The exciter is a shunt or compoundwound dynamo of direct current. In series with its shunt ield winding is connected a resistance. which, preferably, is made variable as is a rheostat. I provide a series of switch contacts, which. when closed, short circuit' the resistance in series with the exciter field winding. these shortcircuiting contacts being intended to regulate o1' control the voltage of the current delivered from the exciter to the tield winding of the synchronous motor. these short-circniting contacts. are neither open nor closed for any very long period of time. Generally they are in rapid vibration, with the result that the resistance in series with the shunt tield winding of the exciter is rapidly cut in and out of circuit. 'hen the resistance is in circuit with the shunt tield winding the iield current of the exciter is reduced, with a consequent drop in the potential of the direct current delivered to the tield of the synchronous motor. Vhen the resistance in series with the exciter field winding momentarily short-circuited the current through the exciter tield winding will increase. with a resulting increase in the iield excitation of the synchronous motor.

The magnetic inertia of the lield of the. ex'

citer is such that the sudden and momentary making and breaking of the short-circuit in shunt ot the tield resistance results in a comparativeiy gradual variation in the magnetof tire short-circuiting contacts ahovewrefcrred to controlled h v a combination of electromagnetic mechanism. inlluenced. priuiariiy. hy thc pressure at the hns hars suppliedL ity the tran-:former whose regulation is under consideration. and. secomlarily. hy the pressure of the current supplied to the field ot the syncnroeous motor. 'this automatic 0rd i na ri ly74 `turns and vice versa.

mechanism will he understood to better advantage hy. reference to the drawings. I may state at this point, however, that the control of the lieto excitation of the synchronous motor eti'ccted in this way will cause the synchronous motor to pick up a more or less leading current, as may he rcquired to maintain a power factor which will give the transformer the requisite regulation.

In the accompanving-diagramnnitic drawing l have illustrated the combination ofmy invention. i

The 12.00() volt buses l and (il are supplied from the generator (i. rthe primary windings A. l and t" ot the three phase. transformer are connected with the 1200() volt buses. as shown. 'l`he secomlary windings Af. Il: and t"` of the thret` phase transformer are connected with the tout) volt feeder huses u. Y; and c. rl`he junction point of the star winding of the secondary windings of the transformer is connected to ground y. as shown. The load circuits L and Il? are shown leading from the tout) volt buses u. I; and c.

The transformer i is constructed in such a way that there will he a large leakage ol magnetic lilies of force hctwecn thc primary and the secondary windings. rl`o this end. the primary and secondarv windings are not closely interlaced. (ln the contrary. the secondary windings are considerahly displaced relative to the primary `windings with the result that a considcrahle proportion of the lines olI t'orcc which link the primary turns do not; thread the secondary l have font d in practice in installations of large power that excellent results are olitaincd when the inipedancc drop of the transformer is brought'l in thisl way to ahont tive per cent'. at full load. former ollsuch high impedance drop is well adapted to withstand the electrical shocks caused hy short-circuit or other derangement. lts regulation is necessarily' poor` however. particularly when the t'ecdcrs L and .lf supply large induction motors which are started from time to time or when. tor any reason7 the power l'actor of the load is low. In accordance with my invention l improve the power factor to a point at which the regulation of the transformer having the large live per cent. impedance drop will lie comparatively good. The armature ot' the three phase synchronous motor S is connected with the vl.()tltl volt huscs it. and c. The, direct current, tield winding Al" of the synchronous motor is supplied with current delivered through the exciter buses fl and The. exciter is shown at 1C. lt is a compound wound d \jinii1|ootl direct current. the. armature heing indicated at r. the, series field .winding at /i and the shunt As previously explained. a trans-v llt) . trolled by a combination of velectromagnetic field, at ji 1t will be noted that the variable resistance R is included in series with the shuntfield winding y' of the exciter. The manually operable regulating switch w can be set to detern'iine the amount of the resistance in series with the shunt winding of the lVitli constant. excitation of the field of the synchronous motor the regula`` exciter.

up fluctuations coming from the generating station as well as the fluctuations due to changes in the load on the line, I provide switch mechanism for intermittently shortcircuiting `t1ie resistance R, which normally is included in circuit with the shunt winding y' of the exciter E. When the resistance R 'is short-circuited the field magnet of the exciter will be strengthened, thereby raising the voltage of thel current supplied to the exciter buses. The fields of the synchronous motor S will therefore be strengthened and the synchronous motor will be made to pick up more of a leading current. iVhen the short-circuit is4 taken off the resistance R the reverse effect will ensue.

In accordance with my invention, the short-circuiting'of the resistance in series with the shunt winding of the exciter is conmechanism acting upon the pairs of switch contacts 1, 2, 3,4 and The effect of the Closure of these contacts is to short-circuit the resistance R. When the contacts are opened the resistance R is included in circuit. These switch contacts are normally in` more or less rapid' vibration and in order that the pressure across any pair of contacts shall not be So great as to cause destructive arciiigthe resistance R is divided up into a number of sections, each section beingconnected with one pair of the contacts. All. of the contacts are, however, opened or.

closed simultaneously. The insulated rod G communicates the motion ofthe bell crank arn'iat-ure 7 to the 4pairs of switch contacts l, Q, 3, 4 and 5. The armature 7 is controlled by a differentially wound relay niagnet S. One winding 9 of this magnet is connected with the exciter A.buses (I an'd bv means of the 4wires 1() and 11. The circuit of the other winding 12 of this differential relay leads through the wire 13 to the lower contact 1l of a pair of fioating contacts, the upper Contact 15 of the pair being connected through the wire 16 with .tlie-"i'egative exciter bus bai'. The floating contacts are under the control of electromagnets, one of which is energized by an alternating current proportional to the pressure on the 1,0 00 volt buses and the other of which is energized by .a current proportional to the vpressure of the current which excites the field of the synchronous motor. The alternating leurrent magnet is indicated at 17. 1t is energized by a current delivered from the potential transformer 18, the primary winding of Y.this transformer being connected, as shown, between one of the 4,000 volt bus bars and ground. The energization of the electroinagnet 17 raises the weight of the core 19 to depress the Contact 14 of the Heating pair. An adjustable eounterweiglit 2&0 more or less `completely balances the weight of the core 1.49. A dashpot 21 steadies the movement of this contact and its electromagnetic controlling mechanism. The upper contact 15 of the fioating pair is controlled by the winding 22 of the direct current electroniagiiet, this winding being connected, as shown, across the exciter bus bars. The energization of this helix draws the core downwardly, theil-eby tending to separate the contacts 15 and 11. An adjustable spring 2l opposes when energi' ed. A stop 25 limits the moveinent of tlie'core 23 when the encrgization of the coil 22 is increased. The electrical and magnetic adjustments are made such that when the exciter field resistance 1i is included in circuit the pressure of the exciter buses will be too low and such that when the resistance 1t is short-circuitedthe pressure on the exciter bus bars will increase to a. point whichis to`o high. 1f we assume now that the pressure of the alternating current on the 4,000 volt bus bars decreases, the

ypotential transformer 1S will deiiver a curthrough the winding 9, with the result that the' armature 7 will be retracted by its spring' he movement of the core 23V i ie to cause the closure of the several pairs of short-circuiting contacts 1, 2, 3, 4 and 5. 1V hen the resistance 1t is cut out of the eircuit of the field winding y' of the exciter, due to the closure of these short-circuiting contacts, the field vstrengthof the exciter will be increased with the result that the exciter will increase the pressure of the current delivered to the field magnet l" by the synchronous motor The increase"in the volta of the exciting currentwill have an immediate effect in increasing the enereivlation of the direct current control magnet 22, which will act to draw in its core 23, thus causing current control magnet 1T.

the floating contact l5 to separate trom lower contact M. The down 'ard movement of the core 2t-lof the direct current control magnet may be limited by the stop 25, thus causing the separation of the lloating contacts to be eti'ected as Jfollows: rlhe incr `ase in the pressure ot the exciter current will canse an increased excitation ot the lield magnets ot the synchronous motor i". This will cause the synchronous motor to pick up a more leading current.. This will improve the power factor of the load on the alternating current transformer. lts regulation will therefore be improved and the alternating current pressure on the 4.00() volt buses will be increased. An increase in the pres sure ol tl alternating currentwill. cause an increased energization ot the alternating The increased energization ot this magnet will raise the. core lll. tending to open the contacts ll and 15. It will be apparent that any drop in the pressure across the exciter buses will decrease the cnergization ot the direct current control magnet 22. thereby tending to bring the lloating contact l5 into engagement with the contact 1l. A\ny drop in the alternating current pressure will tend to bring the contact ll into engagement with the contact l5. \\'hen. however. the pressure has been increased tothe proper point. the lloating contacts will be separated. therehv cutting oll the current supplied to the neutralining winding ot' the di llerential relay. The resulting' attraction o't the armaturei will cause the short-circuit around the resistance it to be removed. 'l`he resistance 1l having thus been included in circuit witlrthe shunt winding ot the exciter` the voltage ot the current delivered by the exciter begins to drop, the llield excitation ot' the synchronous motor drops correspondingly, the lag ot the alternating current load upon the transformer increases and the pressure upon the 4.000 volt bus bar is correspondingly de creased. The various spring tensions and the. counterweight upon the lower contact ot the floating pair are adjusted to maintain the desired voltage. rl`he cycles otl events controlled by the lloating contacts are carried out with extreme rapidity. giving rise rto a vibration ot' the. loating contacts rather than to the slow and gradual '.aovcment which might be interred Yfrom thc above description.

series ot' condensers it. 2T. 2H. 2S) and 2l() serves to reduce the sparking between the pairs ol short-circuiting contacts. "lhe con-V dcnscrs serve also to some extent to smooth out the n'regularlties in the. lield magnet current o'l the exciter. 'l`he magnetic inertia otI the lield magnets issuch that the previ@ ously described changes in magnetism do not take place as suddenly as might be expected. '.l`he result is that the operation ot theme51- tremely sensitive control magnets maintainsl a steady pressure on the exciter bus bars. 'l`his in'essure` while steady. is not uni'lorm. lt varies gradually to maintain sucn a lcgree ot excitation inthe lield ot the synchronous motor that the power tactor oll the transformer load will be varied to cooperate with the transformer itselt in producing a .substantially constant pressure upon the lato() bolt bus bars.

lt will be apparent that variations in presN sure, coming trom the generator station will all'ect the automatic regulating mechanism in a manner corresponding with that already described and to a considerable extent. 'l`heretorethe combination ot my invention will serve to maintain the proper pressure upon mains and tceders` regardless o'l: whether the lluctuations come Vlrom the generating station or Vlrom variations or changes in the character ot the load upon the lines' supplied by the transformer.

Various accessories. such as the rheostatf in circuit with the field winding olE the synchronous motor. will ot' course be applied in :tccordamfc with the well known practice ot the art.

llaving described my invention. Vl claim as new and desire to secure. by Letters lat.- ent:

l. In combination. alternating-current supply mains having a substantially constant electro-motive 'torce impressed thereupon. load circuit mains. a transformer comprising primary and second-.try windings connected to said supply and said load mains. respectively. said transformer being so constructed as to secure snlliciently high magnetic leakage to limit the current on accidental short circuit to a sate value and thereby prevent disruption o'l the trans Vformer. a rotary condenser. such as a synchronous motor connected across said load circuit mains. means 'For over-exciting the lield o'lsaid synchrontms motor to cause the same to draw leading current sullicient to correct the leakage ot' the translormer at a given load. and a regulating device controlled by the voltage on said load mains tor regulating the lield strength ot said rotary condenser to a proper degree.

2. ln combination. three-phase supply llt) mains having asubstantially constant alternating electro-motive torce impressed thereupon three-plaise load mains. transtormer means including primary windings connected to the supply mains. and secondary windings connected to the load mains. cores tor said windings. said. windings being spaced apart on said cores to cause relatively high magnetic leakage between said windings. and thereby to limit short circuit` current to a sate value.. load devices con-A nected to said load mains. a tln'cwllhaaee rotary condenser hex-:re neans to ever-excite mams, and a voltuge-controlled/ regulator 1910. for "overniuf the ielcleXetatin ,fof said -A r rotfuzy condelser to correct tl/l/e magneti@L EDMUND O SLIUVEITAER' 5 leakage in the transformer regardless f they Wltnesses:

value of the load. j E. T. GALLS,

11i witness whereof, I hereunto sub'sfcf/be -W. A. BLIND.

the elcl thereof connected to sidvlo'ad my name this 1st day'of December. A. D., 

